1. Field of the Invention
This invention relates in general to re-polarization means for generating circular polarized electro-magnetic waves using a single or multi-layer lattice structure mounted in front of a radiation aperture and the lattice structure consisting of a plurality of conductors in the form of lines such as meander lines or the like which extend parallel to each other.
2. Description of the Prior Art
Because of the greater ease of construction to obtain linear polarization, primary radiators for example for search and target tracking radar antennas are generally constructed as linear polarized structures. Since the employment of circular polarization is desirable in radar applications so as to reduce reflection effects of rain clouds, the linear polarization of the antenna generally is converted by a lattice structure mounted in front of the antenna aperture to obtain circular polarization. Such polarization converters with lattice structures are shown, for example, in U.S. Pat. No. 3,754,271. According to this patent, meander lines extend at 45.degree. to the E-vector of the incident wave and generate a phase difference due to the capacitance or respectively the inductance effect of the E-vector components which are perpendicular and parallel to them for which the phase difference of 90.degree. necessary for polarization is achieved by using suitable dimensioning and layering.
Other types of lattice structures consist of straight lines at specific intervals in a plurality of layers as well as of line/rectangular combinations for generating circular polarization are known. Suppression or decoupling of the cross-polarization are in general of the orthogonal or de-polarization with respect to a desired linear or circular polarization is of great importance in many applications for example in order to avoid cross-talk wherein double polarization operation exist or in order to achieve the necessary precision in position finding systems. For this purpose, lattices with metal strips or wires extending perpendicular with respect to the E-vector can be employed in a known manner to obtain linear polarization. The cross-polarization component extending parallel to the wires is reflected and, thus, suppressed. By employing a plurality of such lattice layers, the amount of suppression of the cross-polarization components can be further increased.